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Controlling the form of strong converging shocks by means of disturbances.
KTH, School of Engineering Sciences (SCI), Mechanics.
KTH, School of Engineering Sciences (SCI), Mechanics.
KTH, School of Engineering Sciences (SCI), Mechanics.
2007 (English)In: Shock Waves, ISSN 0938-1287, E-ISSN 1432-2153, Vol. 17, no 1-2, 29-42 p.Article in journal (Refereed) Published
Abstract [en]

The influence of artificial disturbances on the behavior of strong converging cylindrical shocks is investigated experimentally and numerically. Ring-shaped shocks, generated in an annular cross sectional shock tube are transformed to converging cylindrical shocks in a thin cylindrical test section, mounted at the rear end of the shock tube. The converging cylindrical shocks are perturbed by small cylinders placed at different locations and in various patterns in the test section. Their influence on the shock convergence and reflection process is investigated. It is found that disturbances arranged in a symmetrical pattern will produce a symmetrical deformation of the converging shockfront. For example, a square formation produces a square-like shock and an octagon formation a shock with an octagonal front. This introduces an alternative way of tailoring the form of a converging shock, instead of using a specific form of a reflector boundary. The influence of disturbances arranged in non-symmetric patterns on the shape of the shockfront is also investigated.

Place, publisher, year, edition, pages
2007. Vol. 17, no 1-2, 29-42 p.
Keyword [en]
shock focusing; annular shock tube; imploding shock
National Category
Fluid Mechanics and Acoustics
Identifiers
URN: urn:nbn:se:kth:diva-7428DOI: 10.1007/s00193-007-0087-9ISI: 000248819100003Scopus ID: 2-s2.0-34547906425OAI: oai:DiVA.org:kth-7428DiVA: diva2:12453
Note
QC 20100706 Tidigare titel: Controlling the form of strong converging shocks(20101126)Available from: 2007-08-31 Created: 2007-08-31 Last updated: 2010-11-26Bibliographically approved
In thesis
1. On focusing of shock waves
Open this publication in new window or tab >>On focusing of shock waves
2007 (English)Doctoral thesis, comprehensive summary (Other scientific)
Abstract [en]

Both experimental and numerical investigations of converging shock waves have been performed. In the experiments, a shock tube was used to create and study converging shock waves of various geometrical shapes. Two methods were used to create polygonally shaped shocks. In the first method, the geometry of the outer boundary of the test section of the shock tube was varied. Four different exchangeable shapes of the outer boundary were considered: a circle, a smooth pentagon, a heptagon, and an octagon. In the second method, an initially cylindrical shock wave was perturbed by metal cylinders placed in various patterns and positions inside the test section. For three or more regularly spaced cylinders, the resulting diffracted shock fronts formed polygonal shaped patterns near the point of focus. Regular reflection was observed for the case with three cylinders and Mach refection was observed for cases with four or more cylinders. When the shock wave is close to the center of convergence, light emission is observed. An experimental investigation of the light emission was conducted and results show that the shape of the shock wave close to the center of convergence has a large influence on the amount of emitted light. It was found that a symmetrical polygonal shock front produced more light than an asymmetrical shape.

The shock wave focusing was also studied numerically using the Euler equations for a gas obeying the ideal gas law with constant specific heats. Two problems were analyzed; an axisymmetric model of the shock tube used in the experiments and a cylindrical shock wave diffracted by cylinders in a two dimensional test section. The results showed good agreement with the experiments. The temperature field from the numerical simulations was investigated and shows that the triple points behind the shock front are hot spots that increase the temperature at the center as they arrive there.

As a practical example of shock wave focusing, converging shocks in an electrohydraulic lithotripter were simulated. The maximum radius of a gas bubble subjected to the pressure field obtained from the lithotripter was calculated and compared for various geometrical shapes and materials of the reflector. Results showed that the shape had a large impact while the material did not influence the maximum radius of the gas bubble.

Place, publisher, year, edition, pages
Stockholm: KTH, 2007. vii, 73 p.
Series
Trita-MEK, ISSN 0348-467X ; 2007:06
Keyword
converging shock, Euler equations, imploding shock, Mach reflection, regular reflection, shock focusing, shock tube
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-4479 (URN)978-91-7178-741-5 (ISBN)
Public defence
2007-09-21, F3, Valhallavägen 79, Stockholm, 10:15
Opponent
Supervisors
Note
QC 20100706Available from: 2007-08-31 Created: 2007-08-31 Last updated: 2010-07-06Bibliographically approved
2. On focusing of strong shock waves
Open this publication in new window or tab >>On focusing of strong shock waves
2005 (English)Licentiate thesis, comprehensive summary (Other academic)
Abstract [en]

Focusing of strong shock waves in a gas-filled thin test section with various forms of the reflector boundary is investigated. The test section is mounted at the end of the horizontal co-axial shock tube. Two different methods to produce shock waves of various forms are implemented. In the first method the reflector boundary of the test section is exchangeable and four different reflectors are used: a circle, a smooth pentagon, a heptagon and an octagon. It is shown that the form of the converging shock wave is influenced both by the shape of the reflector boundary and by the nonlinear dynamic interaction between the shape of the shock and the propagation velocity of the shock front. Further, the reflected outgoing shock wave is affected by the shape of the reflector through the flow ahead of the shock front. In the second method cylindrical obstacles are placed in the test section at various positions and in various patterns, to create disturbances in the flow that will shape the shock wave. It is shown that it is possible to shape the shock wave in a desired way by means of obstacles. The influence of the supports of the inner body of the co-axial shock tube on the form of the shock is also investigated. A square shaped shock wave is observed close to the center of convergence for the circular and octagonal reflector boundaries but not in any other setups. This square-like shape is believed to be caused by the supports for the inner body. The production of light, as a result of shock convergence, has been preliminary investigated. Flashes of light have been observed during the focusing and reflection process.

Place, publisher, year, edition, pages
Stockholm: KTH, 2005. vi, 42 p.
Series
Trita-MEK, ISSN 0348-467X ; 2005:16
Keyword
shock focusing, imploding shock, converging shock, reflected shock, annular shock tube
National Category
Fluid Mechanics and Acoustics
Identifiers
urn:nbn:se:kth:diva-565 (URN)91-7178-207-9 (ISBN)
Presentation
2005-12-15, S40, Teknikringen 8, Teknikringen 8, 10:15
Opponent
Supervisors
Note
QC 20101126Available from: 2005-12-20 Created: 2005-12-20 Last updated: 2011-09-07Bibliographically approved

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